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The small, spherical 68 x 68 - 2 KB reich-chemistry... Dalton's Atomic Theory It was in the early 1800s that John Dalton, an observer of weather and discoverer of color blindness among other things, came up with his atomic theory. Main points of Dalton's Atomic Theory => Elements are made of tiny particles called atoms. => All matter is made of atoms. Atoms are indivisible and indestructible. => All atoms of a given element are identical in mass and properties => The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative atomic weights. => Atoms of one element can combine with atoms of other elements to form chemical compounds; a given compound always has the same relative numbers of types of atoms. Compounds are formed by a combination of two or more different kinds of atoms. => Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together. A chemical reaction is a rearrangement of atoms. PLANETARY MODEL The planetary model may not be the ultimate, perfect model of the atom, but don't underestimate its power. It already allows us to visualize correctly a great many phenomena. Rutherford naturally considered a planetary-model atom, the Rutherford model of 1911 - electrons orbiting a solar nucleus – however, said planetary-model atom has a technical difficulty. The laws of classical mechanics, predict that the electron will release electromagnetic radiation while orbiting a nucleus. Because the electron would lose energy, it would gradually spiral inwards, collapsing into the nucleus. This atom model is disastrous, because it predicts that all atoms are unstable. Also, as the electron spirals inward, the emission would gradually increase in frequency as the orbit got smaller and faster. This would produce a continuous smear, in frequency, of electromagnetic radiation. However, late 19th century experiments with electric discharges through various low-pressure gasses in evacuated glass tubes had shown that atoms will only emit light (that is, electromagnetic radiation) at certain discrete frequencies. The Rutherford Bohr model of the hydrogen atom. In 1913, Rutherford and Bohr pictured the arrangement of the atom's parts to look like our solar system. At the center of every atom is a nucleus, which is comparable to the sun in our solar system. Electrons move around the nucleus in "orbits" similar to the way planets move around the sun. Each orbit around the nucleus represents an energy level, and electrons cannot exist in between orbits. Orbits closer to the nucleus have lower energy. If energy is added, an electron can be "excited" to jump to a higher energy level--an orbit farther from the nucleus. Eventually, though, the electron will return to its original state, and the atom will give off energy equal to the difference between the two orbits. Electron Cloud Model electron orbitals The electron cloud model is a model of the atom wherein electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically-influenced model, we shouldn't know exactly where they are, and hence describe their probable location around the nucleus only as an arbitrary 'cloud'. Plum Pudding Model The Plum Pudding Model is an atom model proposed by JJ Thomson, the physicist who discovered the electron. It is also known as the Chocolate Chip Cookie or Blueberry Muffin Model. You can easily picture it by imagining the said goodies. For example, you can imagine a plum pudding where in the pudding itself is positively charged and the plums, dotting the dough, are the negatively charged electrons. Thus, in contrast to today's atom that has a very dense and very small (compared to the whole atom) positively charged nucleus, Thomson's had a more dispersed positive charge. As a whole, the plum pudding representation only strived to explain why most atoms were neutral.